The present invention relates generally to turbines and particularly to land-based gas turbines for power generation employing closed-circuit steam cooling paths for cooling the hot gas components and returning the spent cooling steam to a return, for example, a heat recovery steam generator used in a combined cycle system.
Steam cooling of hot gas path components, for example, the buckets of a gas turbine, has been proposed in the past and found efficacious in land-based power generating plants. While gas turbines are typically air-cooled, for example, jet engines employ compressor discharge air for cooling the hot gas components, steam cooling is more efficient in that the losses associated with the use of steam as a coolant are not as great as the losses realized by extracting compressor bleed air for cooling purposes. Also, in combined cycle operations, steam cooling is particularly advantageous because the heat energy imparted to the steam as it cools the gas turbine components is recovered as useful work in driving the steam turbine in the combined cycle operation.
In U.S. Pat. No. 5,593,274, of common assignee herewith, there is disclosed a gas turbine having coaxial steam passages for supplying cooling steam to hot gas components of the rotor, for example, the buckets, and returning the spent cooling steam to a return. Various refinements and improvements, however, in the supply and return of the steam for cooling purposes are provided by the present invention.
The present invention provides a closed-circuit steam cooling system for cooling the hot gas path components of the gas turbine rotor and returning the spent cooling steam to a return. In general, the system includes a bore tube assembly for receiving cooling steam from a cooling inlet scroll for passage generally along the axis of the gas turbine rotor. The supplied cooling steam is turned in a generally radial direction for flow through tubes in an aft shaft disk for conveying the cooling steam adjacent the rim of the rotor. The cooling steam is supplied axially along the rim of the rotor by a plurality of supply passages or tubes extending through openings in the stacked wheels and spacers forming the gas turbine rotor. Each supply passage or tube supplies cooling steam to a supply manifold segment, a plurality of which segments are circumferentially spaced one from the other about the rotor. Each supply manifold segment includes a plurality of exit ports and supply passageways for supplying cooling steam to each of first and second buckets of respective turbine wheels, preferably of the first and second stages of the gas turbine for cooling the buckets. Spent cooling steam is returned from the buckets via return passageways and inlet ports to a plurality of return manifold segments circumferentially spaced one from the other about the rim of the rotor. The return manifold segments are each connected to an axial return tube extending along the rim of the rotor to the aft shaft disk. The spent cooling steam flowing axially along the return tubes is supplied to radial tubes extending in the aft disk for return to the bore tube assembly and exit to a return, for example, a heat recovery steam generator of a combined cycle system.
Various aspects of the generally aforedescribed cooling steam system are of particular significance. For example, the flow of the supply and return thermal medium changes between radial and axial directions at the rim of the rotor. Elbows of novel configuration and use are provided in radial opening slots in the aft disk in communication with the axial and radial tubes for changing the direction of flow. For example, elbows are provided interconnecting the radial supply tubes for turning the flow of the supply steam from radial directions into an axial direction in communication with the steam supply tubes along the rim of the rotor. Likewise, elbows interconnect the axial return tubes with the radial tubes for changing the direction of flow of the spent cooling medium from an axial direction to radial directions. The elbows are preferably integrally cast parts readily assembled into the slots of the aft disk.
In another aspect of the present invention, the cooling steam supply and spent cooling steam return manifolds are each provided in circumferentially spaced manifold segments. The supply and return manifold segments are also axially spaced from one another. Each manifold lies in communication with the buckets of a pair of wheels. For example, each supply manifold segment lies in communication with certain buckets of adjacent wheels on opposite axial sides thereof. Likewise, the return manifold segments receive spent cooling steam from certain buckets which also lie on opposite sides of the return manifold segments. Spoolies are used to interconnect the supply and return manifold segments with the various passages in the buckets. Various other aspects of the present invention will become more apparent upon reference to the following specification and drawings.
In a preferred embodiment according to the present invention, there is provided in a turbine rotor having axially spaced wheels mounting buckets, and spacers between the wheels, a cooling system for cooling the buckets, comprising a plurality of cooling medium supply passages circumferentially spaced from one another about and adjacent a rim of the rotor, a plurality of spent cooling medium return passages circumferentially spaced from one another about and adjacent the rim of the rotor, a plurality of supply manifold segments circumferentially spaced from one another about and adjacent the rim of the rotor, each supply manifold lying in communication with at least one of the supply passages for receiving the cooling medium, each supply manifold segment having a plurality of supply ports connecting the supply manifold segment and cooling medium inlets for the turbine buckets of the axially spaced wheels and a plurality of return manifold segments circumferentially spaced from one another about and adjacent a rim of the rotor, each return manifold segment lying in communication with at least of one of the return passages for receiving spent cooling medium, each return manifold segment having a plurality of return ports connecting the return manifold segment and spent cooling medium outlets for the turbine buckets of the axially spaced wheels.
In a further preferred embodiment according to the present invention, there is provided in a turbine rotor having axially spaced wheels mounting buckets, and spacers between the wheels, a cooling system for cooling the buckets, comprising a plurality of generally axially extending cooling medium supply passages circumferentially spaced from one another about and adjacent a rim of the rotor, a plurality of generally axially extending spent cooling medium return passages circumferentially spaced from one another about and adjacent the rim of the rotor, first and second sets of a plurality each of generally radially extending passages for respectively supplying the cooling medium to the cooling medium axial supply passages and returning the spent cooling medium from the spent cooling medium axial return passages, an aft disk forming part of the rotor and having axial extending slots about a periphery thereof and a plurality of flow turning elements disposed in the slots interconnecting the axial and radially extending passages and having passageways for turning flow between generally axial and radial directions.
In a still further preferred embodiment according to the present invention, there is provided in a turbine rotor having axially spaced wheels mounting buckets, and spacers between the wheels, a cooling system for the buckets comprising a plurality of generally axially extending cooling medium conveying passages circumferentially spaced from one another about and adjacent a rim of the rotor and lying in communication with the buckets, a plurality of generally radially extending passages in communication with the axial passages for conveying the thermal medium, an aft disk forming part of the rotor and having axially extending slots about a periphery thereof and a plurality of flow turning elements disposed in the slots interconnecting the axial and radial extending passages and having passageways for turning flow between generally axial and radial directions.
In a still further preferred embodiment according to the present invention, there is provided in a turbine rotor having axially spaced wheels mounting buckets, and spacers between the wheels, a cooling system for cooling the buckets, comprising a cooling medium supply passage extending generally axially along the rotor, a cooling medium return passage extending axially along the rotor, a supply manifold adjacent the rim of the rotor in communication with the supply passage for receiving the cooling medium, the supply manifold having a plurality of supply ports connecting the supply manifold and cooling medium inlets for the turbine buckets of the axially spaced wheels and a return manifold adjacent a rim of the rotor in communication with the return passage for receiving spent cooling medium, the return manifold having a plurality of return ports connecting the return manifold and spent cooling medium outlets for the turbine buckets of the axially spaced wheels and thin-walled spoolies having spherical end portions disposed between (i) the supply manifold and the cooling medium inlets and (ii) the return manifold and the spent cooling medium outlets.